This invention provides a chemical method for the modification of a substrate surface to accomplish heteroepitaxial crystal growth.
The development of new device isolation geometries requires a process to grow semiconducting materials on insulating surfaces. To this end, significant efforts have been directed toward the growth of semiconductors on insulators. Much of this work has been devoted to the growth of silicon (Si) on amorphous silicon dioxide (Atwater et al, Appl. Phys. Lett. 43, 1126-1128 (1983)) and include elaborate seeding techniques to achieve overgrowth of the crystalline silicon. Although this silicon/silicon dioxide interface has acceptable electronic properties, the crystalline perfection of the silicon overgrowth has been inadequate for fabrication of reliable devices.
The heteroepitaxial growth of silicon on sapphire substrates has also been investigated (Ishida et al, J. Appl. Phys. 64, 2087-2091 (1988) and Nakata et al, U.S. Pat. No. 4,546,376.) This silicon/sapphire combination eliminates the need for incorporating a seeding geometry since the sapphire substrate is crystalline. However, these epitaxial layers are characterized by a high density of crystalline defects which result from the large lattice mismatch and difference in thermal expansion coefficients of silicon and sapphire.
Another method to accomplish the growth of a semiconductor (e.g. Si) on an insulating substrate, while avoiding the lattice constant and thermal expansion coefficient mismatch characteristic of the silicon/sapphire system, involves irradiation of a semiconductor substrate so that its bulk becomes semi-insulating, while it retains a semiconducting surface layer (U.S. Pat. No. 4,469,527).
Growth of heteroepitaxial multiconstituent material on a substrate (U.S. Pat. No. 4,477,308) has been accomplished by deposition of a thin layer of a "template forming material" which contains at least one constituent of the multiconstituent material to be grown, but differs from the composition of the substrate. The "template forming material" and substrate are then heated so that the "template forming material" reacts to form a "template material", usually a material having essentially the same composition as the multiconstituent material to be deposited on this "template material".
Recently, interest has shifted to the alkaline earth fluoride compounds (calcium fluoride, strontium fluoride, and barium fluoride) as insulating surfaces for heteroepitaxial crystal growth (Fathauer et al, J. Appl. Phys. 60, 3886-3894 (1986)). These are promising materials because they enable the growth of lattice-matched semiconductor-on-insulator (SOI) structures, FIG. 1 (Zogg et al, J. Electrochem. Soc. 136, 775-779 (1989)).
Although the reliability issues can be solved by the use of appropriate materials combinations, the growth of semiconducting material on low surface energy insulating material is difficult on general thermodynamic grounds (Himpsel et al, Materials Science & Engineering B1, 9-13 (1988)). Without special surface preparation steps, the semiconductor grows in the form of isolated three-dimensional islands.
A technique for two-dimensional epitaxial growth on fluoride compounds has been reported in the literature. It involves exposing the substrate to a beam of electrons and was shown to improve vastly the growth behavior of germanium (Kanemura et al, J. Appl. Phys. 63, 1060-1064 (1988)) and of gallium arsenide (Furukawa et al, Proc. 1988 International Electronic Devices and Materials Symp., Department and Institute of Electrical Engineering, National Sun Yat Sen University, Kaohsiung, Taiwan, 266-269 (1988)) on calcium fluoride.